A magnetic recording and reproducing device comprises a magnetic recording medium and a magnetic head, and data on the magnetic recording medium is read and written by means of the magnetic head. In order to increase recording capacity per unit area on the magnetic recording medium, it is required to increase area recording density. However, decreasing a recording bit length causes a problem that the area recording density cannot be increased due to thermal fluctuation in magnetization of the medium. Generally, influence by the thermal fluctuation will increase as the value of Ku·V/kT is smaller, where Ku, V, k, and T represent a magnetic anisotropy constant, a minimum unit volume for magnetization, a Boltzmann constant, and an absolute temperature, respectively. Accordingly, Ku or V is required to be increased so as to decrease the influence by the thermal fluctuation.
As a solution to this problem, a perpendicular recording method has been developed. The perpendicular recording method records magnetic signals on a double-layered perpendicular medium having a soft-magnetic underlayer with a single-pole head perpendicularly. This method can apply a stronger recording magnetic field to the medium. Therefore, a recording layer of a medium with a large magnetic anisotropy constant (Ku) can be used. Besides, in a magnetic recording medium in the perpendicular magnetic recording method, an advantage of increasing V while keeping the magnetic particle diameter on the medium surface small, or keeping the bit length small has been achieved by growing magnetic particles in the film thickness direction. However, a limit to the thermal fluctuation resistance is predicted even in the perpendicular magnetic recording method if higher-density magnetic recording media are realized in the future.
As an example of recording media suitable for high-density recording, a scheme to align magnetically-isolated magnetic particles regularly and to record one bit per particle, so-called patterned media, is known. This scheme is considered to be advantageous for high-density magnetic recording because noises caused by fluctuation of magnetized state in a bit transition region do not occur and one bit can be made as small as possible until reaching a thermal fluctuation limit. Similarly, discrete tracks which magnetically isolate tracks only and the like are known. These schemes are characterized by that the size of the bit to be recorded in a track width direction is decided in accordance with the size of convexes (lands) of the medium.
FIG. 12 schematically illustrates a relationship between a perpendicular recording head 14 and a magnetic disk 11 and the perpendicular recording. A conventional magnetic head is configured with a lower shield 8, a reproducing element 7, an upper shield 9, an auxiliary pole 3, a thin film coil 2, and a main pole 1 which are laminated in order from the side of the traveling direction of the head (the leading side). The lower shield 8, the reproducing element 7, and the upper shield 9 constitute a reproducing head 24; and the auxiliary pole 3, the thin film coil 2, and the main pole 1 comprise a recording head (a single pole head) 25.
The main pole 1 is constituted by a main pole yoke 1A bonded to the auxiliary pole via a pillar 17 and a main pole tip 1B which is exposed on a flying surface and defines a track width. Magnetic field from the main pole 1 of the recording head 25 forms a magnetic circuit passing through a magnetic recording layer 19 and a soft-magnetic underlayer 20 and entering into the auxiliary pole 3 to record a magnetic pattern on a magnetic recording layer 19. An intermediate layer may be formed between the magnetic recording layer 19 and the soft-magnetic underlayer 20. As a reproducing element 7 of the reproducing head 24, a giant magneto-resistive effect (GMR) element, a tunnel magneto-resistive effect (TMR) element, or the like is used.
Since the head structure shown in FIG. 12 includes the auxiliary pole 3 and the thin film coil 2 between the reproducing element 7 and the main pole 1, the distance between the recording head and the reproducing head becomes large so that format efficiency is disadvantageously deteriorated. Therefore, as shown in FIG. 13(a), a structure has come to be adopted in which the auxiliary pole 3 is provided on the trailing side of the main pole 1. This structure enables to make the distance between the recording head and the reproducing head small. FIG. 13(b) is a view of the flying surface of the magnetic head 24 viewed from the side of the magnetic disk 11. As shown in FIG. 13(b), the shape of the flying surface of the main pole 1 is desirably a trapezoid whose width of the leading side is narrower, taking account of the head having a skew angle.
In addition to the field strength of the recording head, a field gradient in a profile of a perpendicular component of the head field to record a boundary of a recording bit cell, i.e., a field gradient in a profile of a perpendicular component of the head field in the traveling direction of the head is an important factor to realize a high recording density. To accomplish a higher recording density in the future, the field gradient must be increased much more. To increase the recording field gradient, there has been a structure that provides a magnetic substance, i.e., a so-called trailing shield 32 at the trailing side of the main pole 1, as shown in FIG. 14. Further, another structure has been provided in which so-called side shields 33 are also provided on the side surface of the main pole 1.
Similarly, as shown in FIG. 13(a), in the case that the auxiliary pole 3 forming a closed flux path is provided at the trailing side of the main pole 1, the trailing shield 32 and the side shields 33 may be provided, too. As shown in FIG. 15(a), the coil may be a coil which is wound around the main pole yoke 1A and the main pole tip 1B, a so-called helical coil.
In the case of patterned media or discrete media, concavities and convexities are provided on the magnetic recording layer 19 and the soft-magnetic underlayer 20 as shown in FIG. 16 for example. In addition to this, concaves and convexities may be provided on a non-magnetic film and a substrate which are underlayers of the magnetic recording layer. FIG. 16(a) schematically shows a discrete medium on which concavities and convexities (grooves and lands) are provided in its radial direction in order to define tracks along the circumferential direction. In FIG. 16(b), concavities and convexities are provided in the bit direction, too, to define bit patterns.
There have been examples that the substrate is flat and concavities and convexities are provided on the soft-magnetic underlayer 20 and the magnetic recording layer 19 and that concavities and convexities are provided on the magnetic recording layer 19 only. These are disclosed in Japanese Patent Publication No. 2004-259306 and Japanese Patent Publication No. 2004-164492. Japanese Patent Publication No. 6-119632 discloses a technique regarding data erasure on the on-track by data in a stray field, but this is different from the influence to adjacent tracks due to the recording field from the main pole excited by record current, which is considered by embodiments of the present invention.
As described above, in the schemes using media with concavities and convexities provided thereon, the size of the recording bit in the track width direction is defined by the convexities (lands) on the medium. However, similarly to the conventional schemes, the field strength applied to the tracks adjacent to the track to be written in must be decreased to eliminate attenuation and deletion of the magnetized information which had already been recorded in the adjacent tracks.
From the foregoing, it must be required for achieving higher recording density to reduce the record track width without attenuating or deleting the data in the adjacent tracks. This is the problem to be solved in order to realize higher recording density of the magnetic disk drive utilizing the perpendicular magnetic recording. Especially, the inventors have found that, if lands and grooves are formed by providing concavities and convexities in the radial direction on the soft-magnetic underlayer 20, a magnetic flux is concentrated on the edges of the lands on the soft-magnetic underlayer of the adjacent tracks so that the field strength increases.